I am doing a research report on the Desert
Tortoise. What are the historic and current
populations? What are the historic ranges? What
is going on to help protect the Desert Tortoises?
Thanks!

Question Date: 2006-05-22

Answer 1:

The desert tortoise is widely distributed
throughout major portions of the Mojave and Sonora
deserts of California, Nevada, Utah, Arizona, and
of Sonora and Sinaloa, Mexico. Different genetic,
body plan and behavior features within the desert
tortoise species have resulted in the naming of
two major populations; the "Sonora population" and
Mojave population". It is the Mojave population
that is listed as"threatened" by state and federal
agencies. California listed the tortoise as
threatened in 1989, and the US included it in
1990.Historically, the desert tortoise served as a
source of food, medicine and useful material for
Native Americans. Later, tortoises were eaten by
settlers and traders. Before the early 1950's,
many populations reached densities of several
hundred tortoises per square mile.(Tortoise
population is figured out by density measurements:
the number of animals found divided by their land
range.)

The Mojave population lives
mostly in 6 regions, and the numbers of tortoises
in each area (density) vary within the regions.
For example, in 1984 the density of tortoises in
one area ranged from 0 to 250animals for every
square mile. At one Mojave population site in
California, there was a 76% decline between 1979
and 1992. Today, most populations contain no more
than five to fifty tortoises per square mile. It
is difficult to track tortoise populations,
because the tortoises borrow underground in cold
and hot seasons, and can be difficult to find.
Exact numbers on total population are difficult to
calculate, but these population densities have
been generally decreasing.

The populations
have been decreasing due to several
reasons:

Direct tortoise
threats:Collisions with vehiclesIllegal
collectionDisease (mostly from pets released
into the
wild)DroughtsFiresPredators

Indirect
Threats:Habitat loss from construction and
farmingInvasion of non-native plants into
tortoise habitats Pollution of the
atmosphereLandfills and illegal waste
dumpingGlobal warming

Actions have been
taken to provide tortoise protection areas within
their natural habitats, but it is difficult to
quickly measure the effects of the protection
partly because tortoises have long lifespans
(80-100 years!) and take 10 years or more to reach
sexual maturity. Actions include building fencing
along roads and highways to keep tortoises from
being hit by vehicles, and restricting human
access to protected lands. It is a conservation
goal that population densities do not fall below
10 tortoises per square mile, or 50,000adults
total, so that the species will not go
extinct.

Interesting fact: Tortoise dens
can be used by many generations, and some dens in
southern Utah are estimated to be 5000 years old!